Q&A

Ask Away! with Jeff Smith: Investigating Irregular Block Wear Behind the Cam Gear on a SBC

I have a really nice, four-bolt main small block Chevy 350 that I’m about to build into a street 383 with a stroker crank with forged pistons and good rods. During tear-down, I noticed that the flat surface behind the cam gear is worn with an irregular surface. I think I can file this down and polish it but I’m concerned about this removed material will allow the cam to move too far backward. It looks like the groove is around 1/32 inch deep or so, maybe a little less. Is there a thrust bearing or a shim available to space the cam gear out so it will still align with the crank gear?

D.C.

This is not a common problem with small blocks but we have seen it happen. Happily there’s a simple fix for this issue. Don’t worry about sanding or filing this completely smooth, it’s not really critical. The quick answer is that Comp carries a simple, moly-coated shim (full parts list below) that fits between the cam gear and the block that’s only 0.030 inch thick. So if your block is worn slightly—say around 1/32 (0.0315) inchthis will work perfectly.

Even if the worn portion is not that deep, the chain will help to effectively align the gear properly. If you really were concerned, you could add a thin shim between the crank snout and the crankshaft timing gear, but this really isn’t necessary.

Comp also offers a thrust bearing that uses tiny needle bearings called Torrington bearings encased in a cover. This assembly is much thicker at 0.142 inch and will require a specific cam gear. At that point, if you wanted to go this route it would be less hassle to just invest in a performance timing set that includes a Torrington bearing on the back side of the gear. Comp offers a dual roller adjustable timing set that includes this thrust bearing.

If you are concerned about wear in this area on a typical small or big block Chevy, one small trick might help. It’s a common modification to drill a 0.030 inch hole in one of the front oil galley plugs that will spray oil on the timing set while the engine is running. This is a very small hole that will not drastically affect oil pressure and will positively lube the timing set.

You could certainly drill this hole in a steel fitting but it might be easier to drill this small a hole into an aluminum Allen plug instead. We’ve included a PN listing for some aluminum pipe plugs from Summit Racing at the bottom of this post.

Adding the thrust plate and a lube hole will likely prevent any further damage to your small block so that it will be that much more durable for thousands of fun-filled street miles!

Ask Away! Parts List

Production small block Chevy oil galley front holes are fitted with a press-in plug. Any good machine shop can tap these holes for pipe plugs, which is a much better way to go. You can perform this task yourself of course but it obviously must be accomplished before the final assembly so the block can be thoroughly cleaned of all metal shavings. Tap the holes so that the pipe plugs fit flush with the front of the block. You can also drill one of these plugs for the lube hole at the same time. (Image/Jeff Smith)
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3 Comments

  1. I have a 94 GMC k1500 TBI with approximately 165k miles that I tow a 6k trailer, would it be possible for me to just put a bigger cam in it and leave everything else original? If so what size cam and what HP gain could I expect? One owner.

  2. Larry DeVogel says:

    I have seen this on stick shift cars with big power doing road course’s.

  3. jamie cantrelle says:

    You need to use a Torrington bearing it goes behind the camshaft gear.

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